Writing a Series

This week on Hide and Create Joshua Essoe, Debbie Viguie, Michael Sullivan, and Jordan Ellinger talk about writing a book series.
I want to hit on some things to keep in mind when writing a series:
1. Continuation of character history, physical and personality traits. Don’t forget if Liz has that piercing in her left eyebrow or her right eyebrow. Or if Bobby McBoberson comes from Kentucky or Nebraska. Did Grammar Girl introduce Squiggly and Aardvark to each other, or did they meet on their own?
2. How much info do you repeat to remind readers what’s going on or to inform readers who don’t start at the beginning? There is always going to be a little repetition to get people back up to speed, but the trick is to get the balance right. From a reader’s standpoint it really irritates me when I have to read a great deal of repetitive exposition — especially if I’m binge reading.
3. What timescale are you using? Do you have an immutable character who is always ju